The present invention relates to an improvement of a multilayer hybrid circuit which has a laminated printed circuit board including, at least, inductors, capacitors, and resistors in the printed circuit board itself.
Conventionally, electronic components are mounted on the surface of a printed circuit board, and the wiring among the components is effected through printed wiring on the surface of the board. However, the high density mounting of electronic components requires improvements for mounting components, and/or the structure of components themselves.
The U.S. Pat. No. 4,322,698 provides one solution for high density mounting, and discloses a multilayer hybrid circuit which has a laminated printed circuit board which includes an inductor, a capacitor and/or a resistor. Since those components are produced in a board (not on the surface of the board), the size of the system can be miniturized, and high density mounting becomes possible.
FIG. 1 shows such prior multilayer hybrid circuit. In FIG. 1, a laminated body has a plurality of dielectric laminated layers 23 and a plurality of conductive films 24 so that those conductive films 24 and those dielectric layers 23 compose a plurality of capacitors 25.
In FIG. 1, inductors 16 having an internal conductor 14 and a ferrite layer 15 are also provided. In producing an inductor, an U-shaped conductive pattern 14a is printed, next a ferrite pattern which is dielectric is deposited so that a window is kept at the one end of said U-shaped pattern 14a. Next, another U-shaped conductive pattern 14b is deposited on the ferrite pattern so that end of the pattern 14a at the window of the ferrite pattern is connected to the end of the second pattern 14b. Thus, one turn coil is produced by a pair of U-shaped conductive patterns 14a and 14b. By repeating the above process, an inductor with a plurality of turns 14a and 14b is produced. Similarly, another inductor having U-shaped patterns 14c and 14d is produced.
A glass layer 26 is attached on at least one surface of the laminated body 1A, and a resistor network 9 which has a resistor layer 28 and a conductive layer 27 is attached on said glass layer 26. A printed wiring pattern 10 is deposited on at least one surface of the laminated body 1A, and a plurality of side terminals 3 for external connection are deposited on the sides of the laminated body 1A. The conductive pattern 10 is used for mounting an electronic component 22 (for instance an integrated circuit, or a transistor) on the laminated body 1A. The laminated body 1A is produced through a thick film printing process, and a sintering process. An external electronic component 22 is soldered on the conductive pattern 10 by soldering a terminal wire 12 of the component 22 to the conductive pattern 10 by the solder 13.
However, a prior art multilayer hybrid circuit of FIG. 1 has the disadvantage that wiring between a surface component, and a capacitor, an inductor, or a resistor is effected by using a surface printed conductive pattern 10 and a side terminal 3 deposited on the surface of the laminated body. When a complicated external component 22 which has many external wiring pins is mounted on the board, the wiring pattern 10 must also be complicated. Thus, the area or the size of the board for the wiring pattern must be large, and sometimes that area required for wiring is larger than the area for mounting internal passive components. Further, a large number of side terminals 3 must be provided, and the insulation between the side terminals 3 is difficult when the side terminals 3 are so densed.
In order to solve the above problem, the present applicant proposed the structure set forth in the U.S. filing Ser. No. 464,453 and EP filing Ser. No. 90 400 092. That proposal has not layer, but also an inner wiring layer for connection between inner components. The inner wiring layer has a dielectric layer, a conductive pattern deposited on the dielectric layer, and a conductive through hole for connecting electrically conductive patterns on different dielectric layers.
The present invention is an improvement on said previous invention.
The present invention improves in particular that a through hole is improved in a specific structure with high operational reliability.
Another disadvantage of a prior multilayer hybrid circuit is that it is difficult to provide an inductor with high inductance. As the inductance depends upon the number of windings of a coil, the number of the windings must be large when the inductance is high, and that large number of windings results in an increase of the thickness of the hybrid circuit. Therefore, a thin structure having large inductance has been desired.